Is Reverse Only Letters easy or hard?

Reverse Only Letters is classified as an Easy problem. It mainly tests understanding of string traversal and the two pointer pattern, which makes it a common early interview or practice problem.

Reverse Only Letters Python/Java solution

In Python or Java, convert the string into a mutable character array and apply the two pointer technique. Move pointers inward while skipping non-letter characters and swap letters when found. The implementation runs in O(n) time and uses constant extra space.

How to solve Reverse Only Letters in O(n)?

Use the two pointer technique. Convert the string to a character array, place one pointer at the start and another at the end, and skip any characters that are not alphabetic. When both pointers point to letters, swap them and continue until the pointers cross. This guarantees a single linear pass.

What is the best approach for Reverse Only Letters?

The two pointer approach is the best solution. Start one pointer at the beginning and another at the end of the string, skipping non-letter characters and swapping letters when both pointers land on alphabetic characters. This processes the string in O(n) time and uses O(1) extra space.

Is Reverse Only Letters asked at Google/Amazon/Meta?

Problems involving string manipulation with two pointers appear frequently in interviews at companies like Amazon, Google, and Meta. While this exact question may vary, the pattern of skipping characters and reversing selected elements is a common interview theme.

What data structure is used in Reverse Only Letters?

The optimal method primarily uses the two pointer technique on a character array. An alternative implementation uses a stack to store letters and reconstruct the string in reverse order while leaving non-letter characters unchanged.

What is the time complexity of Reverse Only Letters?

The optimal solution runs in O(n) time because each character is examined at most once while the two pointers move toward the center. A stack-based implementation also runs in O(n) time but requires O(n) additional memory to store letters.

Description Hints 1 Solution Video 7:35

917. Reverse Only Letters

Easy68.9% acceptance5 companies

Given a string s, reverse the string according to the following rules:

All the characters that are not English letters remain in the same position.
All the English letters (lowercase or uppercase) should be reversed.

Return s after reversing it.

Example 1:

Input: s = "ab-cd"
Output: "dc-ba"

Example 2:

Input: s = "a-bC-dEf-ghIj"
Output: "j-Ih-gfE-dCba"

Example 3:

Input: s = "Test1ng-Leet=code-Q!"
Output: "Qedo1ct-eeLg=ntse-T!"

Constraints:

1 <= s.length <= 100
s consists of characters with ASCII values in the range [33, 122].
s does not contain '\"' or '\\'.

Asked at 5 companies

Tanium Snowflake

Google Amazon Microsoft

Topics

String Two Pointers

Hints open one at a time

Hint 1

This problem is exactly like reversing a normal string except that there are certain characters that we have to simply skip. That should be easy enough to do if you know how to reverse a string using the two-pointer approach.

7:35

Still stuck?Read 3 approaches, or watch a walkthrough.

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